1. Field of the Invention
The present invention relates to a method for welding together two bodies, for instance pipes or plates, which are placed mutually in line against each other while leaving clear a weld groove, wherein the weld groove is filled with more than one welding layer by means of a welding torch moved in longitudinal direction of the weld groove. The present invention also relates to a device for welding together two bodies, for instance pipes or plates, which are placed mutually in line against each other while leaving clear a weld groove, comprising at least one carrier for a welding torch guidable in longitudinal direction of the weld groove.
2. Description of the Related Art
It is generally known to realize connections between two pipes, for instance to form a pipeline, or two plates by means of welding. Since the maximum thickness of a welding layer which can be deposited is limited and the pipes or plates are often too thick to be connected with a single welding layer, a welded connection is built up by laying several welding layers over each other until the weld groove is wholly filled. A method and device suitable for this purpose is known from the Netherlands patent application 9400742.
The present invention has for its object to improve the above stated method and device.
The method according to the invention is characterized for this purpose in that two welding layers are laid in one welding pass by means of two welding torches placed successively on a carrier in the longitudinal direction of the weld groove. A time-saving is hereby obtained in the welding process. This is of particular importance in applications where the wielding time is of great economic influence, such as is the case in laying pipelines. Particularly in the use aboard a pipe laying vessel, a short welding time is important in achieving a high production in the number of welded connections per day with a limited number of welding devices. This is because the number of welding devices is limited by the dimensions of the ship.
If the weld groove has outward diverging walls, at least the trailing torch preferably performs an oscillating movement. A wider welding layer can hereby be laid by the trailing welding torch.
When the weld groove is filled with two welding layers in only one welding pass, oscillation of only the trailing welding torch can suffice. If on the other hand the weld groove is filled in several welding passes, both the leading and trailing welding torch are then oscillated. In this latter case the trailing welding torch is preferably oscillated at a greater amplitude than the leading welding torch, so that the width of the welding layer to be deposited per welding pass by each welding torch can be adjusted to the width of the weld groove.
In order in this case to enable complete filling of the weld groove with welding material, wore welding material can be added to the trailing welding torch, although the trailing welding torch can also be oscillated at a different, preferably higher, frequency than the leading welding torch. The field width of the two successive welding layers is separately controlled in that both the amplitude and the frequency of the oscillation movements of the two welding torches, can by individually adjusted and controlled. This provides the advantage that there are far fewer limitations in the choice of the form of the welding seam, and that the welding parameters for both torches an be optimally adjusted, whereby optimum savings are achieved in the welding time without great concessions having to be made in the weld quality (defects, mechanical properties).
In a preferred embodiment of the method for welding together two pipes, two carriers each having two welding torches are moved in peripheral direction of the pipes, thereby achieving a still further saving in the welding time.
The two carriers each having two welding torches can be displaced successively in the peripheral direction of the pipes, but in preference each carrier is moved per welding pass over half a peripheral part of the pipes.
Each carrier is then preferably moved per welding pass in downward peripheral direction of the pipes. When particular welding processes are used, such as MIG/MAG welding, downward welding can be performed at higher speed than upward welding. The total welding time in the connection of two pipes is therefore less if welding takes place in only downward direction and each carrier is returned to its starting position after each welding pass than if welding takes place downward and then upward.
The present invention likewise relates to a device for welding together two pipes or plates. The device according to the invention is characterized by two welding torches lying successively in the longitudinal direction of the weld groove. A significant advantage of this device is that it is compact and thereby suitable for welding together pipes of small diameter or plates of small size.
In this case the weld groove has outward diverging walls, the device according to the invention preferably comprises means for moving at least the trailing welding torch reciprocally in transverse direction the weld groove. These means can for instance be formed by a shaft pin driven for reciprocal sliding in the carrier and connected to the welding torch.